1. Field of the Invention
The present invention concerns a hard disk drive (HDD) for magnetically reading and writing digital data, and more particularly to a technique for measuring the track pitches of a hard disk drive to detect more accurately the position error signal on each disk.
2. Description of the Related Art
Generally, the value of a position error signal (PES) captured by detecting the HDD's burst signals is determined by the resolution of the analog/digital (A/D) converter. The maximum and minimum values of the PES are also determined by the resolution of the A/D converter.
Therefore, the percentage value of the PES is determined not by the actually measured track pitch, but only by the absolute value(constant) based on the resolution of the A/D converter. Usually, the track pitch may vary depending upon the margins of the heads, the characteristics of the recording medium and the servo write and the like. Accordingly, when the track pitches vary according to apparatuses, circuits or environment, the accuracy of the percentage values of the PES can't be guaranteed. Therefore, in order to obtain the accuracy of the percentage values of the PES, it is desirable to measure the track pitch.
The desired track pitch measurement can be conveniently executed by randomly selecting a head and a cylinder from among a number of heads and cylinders. However, the accuracy of such measurement method is only guaranteed on the assumption that the burst signal amplitudes of any inner, mid and outer zones on any one of disks are the same, and the flying heights on each of the zones and the read margins of any one of the heads are also the same.
However, the assumptions differ from the practice. Namely, the amplitudes of the burst signals and the flying heights of the heads vary depending on the inner, mid and outer zones, and the read margins of the heads are different by bits. Consequently, when measuring the track pitches by randomly selecting heads and cylinders, there are measuring errors depending on the characteristics of the heads and cylinders. If the errors are very small, they can be ignored, but if the errors are greater, they may present serious problems. For example, if the detected PES exceeds the specified limit, off-track writing may be caused. Therefore, it is necessary to provide for the track pitch measuring errors.
The following patents each disclose features in common with the present invention but do not teach or suggest the specifically recited technique for measuring the track pitches of a hard disk drive to detect more accurately the position of signal on each disk of the present invention: U.S. Pat. No. 5,581,420 to Chainer et al., entitled Method And System For Determining A Radial Positioning Valve Used For Writing Tracks At A Desired Track Pitch, U.S. Pat. No. 5,146,373 to Wakui et al., entitled Information Signal Reproducing Apparatus With Function Of Detecting Track Pitch, U.S. Pat. No. 4,843,491 to Otokawa, entitled Recording And Reproducing Apparatus With Track Pitch Detection, U.S. Pat. No. 5,241,433 to Anderson et al., entitled Disk Drive Servo Control, U.S. Pat. No. 5,576,909 to Dierkes et al., entitled Method For Positioning A Data Transducer Head In A Rotating Disk Drive Data Storage Device, and U.S. Pat. No. 5,109,306 to Mase et al., entitled Track Access Control System For Magnetic Disk System With Periodic Track Offset Update.